Oxymercuration-demercuration of alkenes involves following steps :
(i) Dissociation of mercury (II) acetate
$CH _{3} COO - Hg - OCOCH _{3} \longrightarrow \underset{\text{electrophile}}{CH _{3} COO - Hg ^{+}}+ CH _{3} COO ^{-}$
(ii) Attack of electrophile on double bond of alkene
(iii) Addition of water
Hence, oxymercuration-demercuration process involves, reduction and bridged mercurinium ion formation.
